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MAE 5310: COMBUSTION FUNDAMENTALS

MAE 5310: COMBUSTION FUNDAMENTALS. Adiabatic Combustion Equilibrium Examples September 19, 2012 Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk. ADIABATIC COMBUSTION EQUILIBRIUM. Previously we have considered:

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MAE 5310: COMBUSTION FUNDAMENTALS

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  1. MAE 5310: COMBUSTION FUNDAMENTALS Adiabatic Combustion Equilibrium Examples September 19, 2012 Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk

  2. ADIABATIC COMBUSTION EQUILIBRIUM • Previously we have considered: • Known Stoichiometry + 1st Law (Energy Balance) → Adiabatic Flame Temperature • Problems 1-4 • Known P and T + 2nd Law (Equilibrium Relations) → Stoichiometry • Problems 5-9 • Now we can combine these: • 1st Law (Energy Balance) + 2nd Law (Equilibrium Relations) → Adiabatic Flame Temperature + Stoichiometry • Problems 10-14 • Solution Scheme • Guess a T=Tguess • Do equilibrium calculation to solve for species concentrations at Tguess • Plug into 1st Law • We want F(Tguess)=0 • If F(Tguess) > 0, then initial guess was too high • If F(Tguess) < 0, then initial guess was too low • Increment Tguess

  3. PRACTICAL APPLICATION: RECUPERATION • A recuperator is a heat exchanger in which energy from a steady flow of hot combustion products, called flue gases, is transferred to the air supplied to the combustion process

  4. SOME COMMON TYPES OF RECUPERATORShttp://www.hardtech.es/hgg_tt_hrt.0.html Tubes cage radiation recuperator Tubes cage radiation recuperator working at 1,200ºC Double shell radiation recuperator Installation consisting of a tubes cage recuperator and a double shell one, series-connected

  5. EXAMPLE: RECUPERATION (TURNS) A recuperator, as shown in figure, is employed in a natural-gas-fired heating-treating furnace. The furnace operates at atmospheric pressure with an equivalence ratio of 0.9. The fuel gas enters the burner at 298 K, while the air is pre-heated. • Determine the effect of air preheat on the adiabatic flame temperature of the flame zone for a range of inlet air temperatures from 298 K to 1,000 K. • What fuel savings result from preheating the air from 298 K to 600 K? Assume that temperature of flue gases at furnace exit, prior to entering recuperator, is 1700 K, both with and without preheat. Radiant-tube burner with coupled Recuperator for indirect firing. Note that All flue gases pass through the recuperator Source: Turns, An Introduction to Combustion

  6. NASA CEA PRACTICE PROBLEM Consider combustion of a methane-air mixture at 10 atm (both fuel and air are at 10 atm). • Plot mole fractions, ci, for the species CO2, CO, H2O, H2, OH, O2, N2, NO vs. temperature for f=1 for a temperature range from 1000 to 2500 K. • Calculate Tflame and mole fractions as a function of f for adiabatic combustion. Plot these results vs. f and discuss at what value the peak flame temperature occurs. Comment on this value in light of the discussion found in Chapter 1, Part 2 of Glassman. • Compare Tflame from part (2) to what would be obtained assuming complete oxidation (burning in only oxygen) and what would be obtained assuming complete combustion (burning in air).

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